Nitrogen spray refrigeration system for perishables

ABSTRACT

A system for more efficient refrigeration of perishable products in trucks and railcars is provided by spraying cold fluid into the product chamber at effective flow rate resulting from maximum flow rating between 30 and 110 lbs. per hour equivalent pure nitrogen per 10 foot average length of storage chambers having cross-sectional area between 40 and 110 ft2, and through spaced small openings in a spray conduit of between 0.002 and 0.009 inch2 per 10 foot average length.

United States Patent Jehle I [451 Dec. 12, 1972 [54] NITROGEN SPRAYREFRIGERATION SYSTEM FOR PERISHABLES [72] Inventor: William RobertJehle, Williamsville,

[73] Assignee: Union Carbide Corporation, New

York, N.Y.

[22] Filed: Oct. 22, 1969 121] App]. No.: 871,797

Related US. Application Data [62] Division of Ser. No. 776,331, Nov. 18,1968, abandoned.

[s2] U.s.c1 .i ..62/223, 62/514 [511 Int.Cl ..Fd3/10 [58 Field ofSearch.......;.....62/514, 64, 45, 373, 223

g [56] References Cited UNITED STATES PATENTS 3,287,925 11/1966 Kane eta1 ..62/5l4 X 3,413,818 12/1968 Pelmulder ..62/64X 3,281,075 10/1966Smyers,Jr. ..62/5l4X Primary Examiner-William E. Wayner Attorney-Paul A.Rose, Thomas I. OBrien, John C.

'LeFever and Lawrence G. Kastriner [5 7] ABSTRACT A system for moreefficient refrigeration of perishable products in trucks and railcars isprovided by spraying cold fluid into the product chamber at effectiveflow rate resulting from maximum flow rating between and 110 lbs. perhour equivalent pure nitrogen per 10 foot average length of storagechambers having crosssectional area between and ft*, and through spacedsmall openings in a spray conduit of between 0.002 and 0.009 inch per 10foot average length.

6 Claims, 2 Drawing Figures PATENTEU 2 I97? 3, 705. 500

INVENTOR WILLIAM ROBERT JEHLE l NITROGEN SPRAY REFRIGERATION SYSTEM FORPERISIIABLES BACKGROUND OF THE INVENTION for highly efficientnitrogen-rich liquefied gas intransit refrigeration of perishableproduct wherein the refrigerant is sprayed into the product chamber.

' The intransit refrigeration of perishables by spraying cold cryogenicliquid from a liquefied gas storage body into the perishable productstorage chamber iswidely practiced as described in Kane et al. U.S. Pat.No. 3,287,925. The conventional practice has been to use sufficientlyhigh maximum flow ratings of refrigerant for rapid cooldown of theproduct storage chamber following initial product loading ordoopopenings, i.e. greater than 200 lbs. perhour liquid nitrogen per footaverage length of chamber. In this manner the cryogenic liquid spraysystem could minimize the period a perishable product, e.g. lettuce, isexposed to highambient temperatures at which deterioration isaccelerated. This was recognized asna significant advantage overmechanical refrigeration systems where the cooldown rate is severelylimited by the need to mechanically circulate environment gas overcooling coils and thereafter refrigerate the product with the cooledgas.

Certain problems have developed in connection with the prior art liquidnitrogen spray refrigeration system, including relatively high liquidnitrogen consumption rates. This necessitated refilling of the liquidnitrogen storage container at more frequent intervals than wasconvenient or economically desirable. Another problem was that therelatively high refrigerant flow rates made it more difficult tomaintain substantially uniform temperatures through the entire length ofthe product chamber. The flow of refrigerant is normally controlled inresponse to temperature sensing means, e.g. a thermostat, positionedwithin the gas space of the product storage chamber so that therefrigerant on cycles required to reach the thermostat set pointtemperature were relatively short. During these periods the chambersections and product closest to the openings in the overhead sprayconduit tended to be overcooled while the remote sections wereundercooled.

It is an object of this invention to provide an improved method of andapparatus for cold nitrogen-rich spray refrigeration of perishables.

Another object is to provide such method and aplimit the heat inleakrate to below 0.10 Btu[hr.l".ft inside surface area. 1

The gas temperature within the storage chamber is monitored, as forexample by a temperature sensing bulb or thermocouple, and cold fluid isdispensed from the storage container in'response to the monitored gastemperature. This cold fluid (either liquid or gas) is sprayed as amultiplicity of discrete streams spaced from each other along the lengthof the storage chamber for refrigerating the perishable product therein.The effective rate of dispensing is that provided bya spray headerhaving maximum continuous flow rating of between and 110 lbs. per hourequivalent pure nitrogen per 10 feet average length of chamber forchamber cross-sectional area between 40 and 100 ft so as tomaintain themonitored gas temperature in a selected temperature range of l0 to 60F.This flow rate is of course far below the aforementioned 200 lbs. perhour nitrogen per 10 foot average chamber length maximum flow ratingcharac V teristic of present intransit spray'nitrogen refrigerationparatus in which the nitrogen-rich liquid consumption SUMMARY In themethod aspect of this invention, pressurized nitrogen-rich liquefied gasis provided in a thermally insulated storage container associated with aproduct storage chamber having thermal insulation sufficient to systems.Tests have indicated that under some operating conditions this inventionpermits about 30 percent reduction in nitrogen refrigerant consumptionover sustained periods with no noticeable loss of product refrigerationeffectiveness.

In the apparatus of this invention,the aforedescribed liquid nitrogenstorage container and product chamber are provided along with sprayconduit means positioned within the upper portion of the storage chamberand extending substantially the entire length thereof. Openings ofequivalent diameter less than 0.07 inch are spaced along the sprayconduit length for discharging a multiplicity of discrete cold fluidstreams into the storage chamber. The openings have a total area ofbetween 0.002 and 0.009 inch per 10 foot average length of chamberwhereas the prior art employed substantially higher opening total areas.At areas below 0.002 inch/l0 ft. average length, insufficient nitrogenrefrigerant flow would be provided into the storage chamber to recoverfrom heat inleak due to door openings within a reasonable period oftime.

In this apparatus, fluid discharge conduit means communicate at one endwith the liquid nitrogen container and at the other end with theoverhead spray conduit. Fluid control means are provided comprising atemperature sensing element positioned within the storage chamber and acontrol valve operably interposed in the fluid discharge conduit means.The control valve is connected to the temperature sensing element to beresponsive to the storage chamber temperature.

The term .average length of chamber is used herein because a particular10 foot section of chamber length may not have the nitrogen-rich flowrate or spray opening total area required to practice the method andapparatus of this invention. The aforementioned ranges are based on thetotal nitrogen-rich flow rate or spray opening area divided by one-tenthof the chamber length used to store product.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view taken incross-sectional elevation of a truck or semi-trailer incorporating oneembodiment of the invention.

FIG. 2 is a schematic view taken in cross-sectional elevation of arailroad car incorporating an alternative embodiment having gascirculating means.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, FIG.1 illustrates an embodiment in which a mobile thermally insulatedstorage chamber 11 is provided for holding perishable product 12. Thischamber 11 may be of standard construction for typical mobilerefrigerated chambers, e.g. reinforced aluminum siding outer walls,plywood panelled inner walls and asbestos or plastic foam insulatingmaterial between the two walls. The thermal insulation 13 must besufficiently effective to limit the atmospheric heat inleak rate below0.l Btu/hr.F.-ft inside surface area, typical materials providingoverall heat conduction rates of about 0.05-0.07 Btu/hr.F. ft A higherquality thermal insulation is not economically justified because thechamber is not airtight, access means such as rear doors being requiredfor insertion and removal of the refrigerated perishable product.

A thermally insulated container 14 is associated with product chamber 11for storing pressurized liquid nitrogen or nitrogen-rich liquid such asair. The term equivalent pure nitrogen" as used herein refers torefrigeration content, as compared to liquid nitrogen. Because thethermodynamic properties of liquid air and nitrogen are vso similar,they are considered equivalent for purposes of this invention.

The construction of container 14 is well-known and usually includes anouter shell completely surrounding an innerstorage vessel to form anevacuable insulation space therebetween, as for example depicted inLoveday et al US. Pat. No. 2,951,348. This space is preferably filledwith an efficient solid insulating material, as for example alternatelayers of radiationimpervious barrier such as aluminum foil separated bylow conductive fibrous sheeting, as for example glass fibers describedin U.S. Pat. No. 3,007,596 to L. C. Matsch. To remove gas accumulatingin the evacuated insulating space, an adsorbent material such as calciumzeolite A or a gettering material such as powdered barium may beprovided therein to retain a high level of insulating quality.

The vessel within storage container 14 is filled with liquid nitrogen bymeans well known to the prior art, such as for example connecting asource of liquid nitrogen stored at above atmospheric pressure to thecontainer. If the liquid nitrogen is stored at a pressure below theoperating pressure of container 14, a suitable pump would be employedand usually additional heat would be added to the pressurized liquidbefore transferring it into container 14. The liquid nitrogen ispreferably charged into container 14 and stored therein at saturatedconditions and at temperatures corresponding to a vapor pressure abovepsig. with the entire liquid and vapor substantially in equilibrium. Ifthe aforementioned highly efficient insulation is used, there is noappreciable amount of heat inleak to the inner storage vessel ofcontainer 14 and the stored liquid nitrogen is dispensed only by thisas-charged vapor pressure. Alternatively the liquid nitrogen may becharged to container 14 under non-saturated conditions and even in thesubcooled state. Under these circumstances it would probably benecessary to provide means for building sufiicient internal pressure ondemand to discharge the liquid. Those skilled in the art will appreciatethat this heat may be introduced externally, using the wellknownpressure building coil. The latter includes a liquid discharge conduit,an atmospheric heat vaporizer and a conduit for returning the resultingvapor to the container gas space (not illustrated). As still anothervariation known to the art, a less efficient heat insulating materialmay be used so that sufficient atmospheric heat inleak is available tovaporize sufficient stored liquid refrigerant to form gas pressure toinsure liquid discharge on demand.

It is preferred to store the liquid nitrogen refrigerant at pressurebelow about psig., because at higher pressures the spray conduitopenings would be impractically small, and also inherent lagcharacteristics of presently known temperature sensing elements wouldmake adequate control of the liquid refrigerant withdrawal moredifficult. The storage pressure is preferably above about 10 psig. toprovide sufficient driving force for substantially uniform distributionof cold fluid through the spray orifices. Storage container internalpressures of 15-22 psig. are commonly used.

Liquid discharge conduit 15 is joined at one end to storage container 14and has control valve 16 therein as part of a liquefied gas flow controlsystem. The latter includes temperature sensing element 17, as forexample a bulb positioned within the storage chamber 11 gas space. Thisbulb is connected by signal transmitting .means 18 to temperaturecontroller 19, and signal transmitting means 20 provides communicationbetween the controller and control valve 16 in liquid discharge conduit15. The flow control means may be electrically or pneumaticallyoperated.

The other end of liquid discharge conduit 15 is joined to overhead sprayconduit 21 having a series of spaced openings 22 therein. Spray conduit21 preferably extends substantially the end-to-end length of productstorage chamber 11 for discharge of cold fluid into such chamber as amultiplicity of discrete streams. Openings 22 may be oriented eitherhorizontally or slightly downwardly in the conduits circumference, andare distributed along the conduit to provide total area of between 0.002and 0.009 inch per 10 foot average length of chamber. Openings 22 may beof any shape, although a circular configuration is preferred for uniformsymmetrical discharge of sprayed refrigerant. The openings should havean equivalent diameter of less than 0.07 inch, i.e. an area smaller thanthe area of a circle of this diameter. Holes of 0.07 inch equivalentdiameter or larger would be so few in number and so widely separatedthat the individual fluid spray streams would be isolated. With suchlarge holes the refrigerant could not be introduced in a uniform patternfrom one end to the other end of the chamber over the product and thusprovide uniform cooling and temperature distribution.

In a preferred embodiment the total area of the spray openings isbetween 0.004 and 0.008 inch per 10 foot average length of the productchamber.

It should be understood that the flow rating of 30-110 lbs. per hourequivalent pure nitrogen per 10 foot average length of chamber, requiredby the method of this invention, is the maximum rate which mightbeemployed with the control valve continuously open, and not theeffective flow rate experienced while the control valve is open duringnormal cycling operation. As used herein, the term effective flow-rate"is from one end: 10, 21, 36, and 51 inches. Whereas the heretoforeemployed nitrogen spray conduits had 1/16 inch diameter (0.0625 inch)circular holes, it has been discovered that smaller size openingsdischarge a more defined as the total refrigerant flow divided by thecon- 5 finely divided liquid Spray whidl in tum affords more trol valveopen time. This includes the. refrigerant uniform l'efrigeratimldistributim beneath the used to initially cool-the product to thedesired low openings- Tests a shown a with even Very long temperaturelevel and the refrigerant consumed to spray conduits (40-45 feet), thePressure drop is recool'the product to this level following warmup dueneghglble so that each 0038411911 Opening Passes I" to periodic openingof the chamber doors. The reason Proxlmately equal quantity of coldnitrogen fluid why the maximum flow rating criteria is used is that itmg Operatlonelim nates variations such as cycle on time due to the Theaforedescribed spray conduit sections have been amb ent temperature. Theeffective flow rate during connected together for use according to thisinvention, cycling operation is affected by the ambient temperainvarious size trucks (about 56 ft cross-sectional area) ture, 1.e. higherfor relatively high ambient temperature and railroad cars (about-95 ft.cross-sectional area) as and lower for'relatively low ambient. Testshave shown 4 listed in Table i TABLE A Unlnsulated spray conduits NumberTotal Area of Max. unit r v standard No. and Total holes, Mex. flowrating spray- Y Dlarn. Areaof in. /10 ft. flow per 10 ft. Productchamber sections spray holes, lgth., rate, lgth. avg., length, ft. usedholes in. average 1b./hr. lb. /hr.

2 s-.0ss" .0001 .0076.0045 120 100-00 3 12-. 03s" .0130 0057-0050 16570-00 4 16-.038 .0181 0060- 0045 210 70-52 5 00s" .0272 70-00 that for aparticular spray header and liquid nitrogen storage container dischargepressure, the refrigerant flow rate increases with on time up to amaximum continuous rate. When the control valve is-first opened and thespray header is warm, it initially discharges virtually 100 percent gas.As the spray header cools down with time, an increasing percentage ofliquid is discharged through the openings. After continuous operation of-90 minutes (depending upon flow rate and heat capacity of the sprayheader) the system reaches substantially stable equilibrium conditionand the spray header discharges virtually 100 percent liquid. The flowrate under such stable condition is the maximum rating as used herein.In a preferred embodiment of the present method, the aforementionedmaximum flow rating is 40 to 90 lbs. per hour equivalent pure nitrogenper 10 foot average length of product storage chamber.

In the normal cyclic operation the temperature controller usuallyterminates refrigerant flow before the maximum rate is reached, and ithas been found that the effective flow rate of an uninsulated sprayheader is on the order of 50-80 percent of its maximum continuousrating. Accordingly, the total area of the openings should be sufficientso that the desired refrigeration may be obtained at the effective flowrate.

he preferred embodiment the spray conduit with spaced openings isprovided in sections of standard length which can be joined end-to-end,depending on the length of product storage chamber. The latter may berelatively short, as for example the 8-10 foot truck body section of anice cream local delivery truck, or very long, as for example a 40 footsemi-trailer or 50 foot long railway cars. The preferred sections foruninsulated spray conduits are composed of A inch IPS brass pipe 57inches long with four 0.038 inch diameter circular holes spaced ll to 15inches apart. In particular, the four holes are located the followingdistances It should be noted from the foregoing table that the totallength of the standard sections for any particular product chamber isnot necessarily equal to the length of the product chamber. In suchinstances, portions of blank pipe (without openings) are used to connectthe standard sections of spray conduit. For example, a 2 foot long blankpipe may be placed between two standard 57 inch long spray sections fora 17 foot chamber, and a 4 foot long blank pipe may be positionedbetween two standard sections for a 20 foot long chamber.

In operation, liquid nitrogen is discharged from storage container 14through conduit 15 to overhead spray conduit 21 and thence throughopenings 22 into chamber 11 for refrigerating perishable product 12.Refrigerant flow is responsive to the chamber temperature as sensed byelement 17. The controller 19 is set to maintain the chamber temperaturewithin a predetermined range, depending on the nature of the product.For frozen commodities, as for example ice cream, the temperature shouldbe about 0-10F. whereas with freeze-sensitive commodities such aslettuce, the temperature should be 35-45F. It should be understood thatthis invention may be employed to refrigerate any type oftemperature-sensitive product irrespective of whether the product is tobe maintained in the frozen or unfrozen state.

The cold nitrogen fluid may be discharged through the spray openings 22as a liquid, liquid-vapor mixture or entirely vapor, depending on theheat transfer characteristics of the particular system. For example, inthe FIG. I embodiment only a relatively small portion of the liquidnitrogen discharged from container 14 is vaporized by heat from theenvironment gas upstream I the openings. In other systems contemplatedby the inven'tion, a heat exchanger may be provided upstream of sprayheader 21 to vaporize part or all of the liquid nitrogen. Such a heatexchanger may be located within or outside the product chamber.

Another contemplated variation is a spray header with thermalinsulation. Whereas non-insulated spray headers are satisfactory forsystems refrigerating frozen products, it may be desirable to positionthermal insulation around the spray header for systems refrigeratingfreeze-sensitive products, e.g. fruits and vegetables. This is becausehigh convective heat transfer to the cold non-insulated spray header maycause freeze damage to the nearby freeze-sensitive products. Also,dripping water from ice frozen on the spray header during operation maydamage product cartons and is annoying to unloading personnel.

Although the spray header may be located anywhere within the upperportion of the product storage chamber, it is preferably located alongthe upper portions of a side wall near the ceiling. In this location,all spray openings are placed along one sideof the header and preferablydirected approximately horizontally across the product, and if moistureforms it will drip down along the wall of the storage chamber.

In certain types of cold nitrogen-rich spray intransit refrigerationsystems, usually those equipped with'thermally insulated spray conduits,means are provided to circulate the product chamber environment gas formore uniform end-to-end temperature distribution. The need for gascirculation means, e.g. a fan, is greatest in long haul service (e.g.over 400 miles between loading and unloading points or requiring transittime greater than about 48 hours) and in particular in relatively longchambers containing products to be refrigerated at above freezingtemperature to avoid deterioration. The fan may be electrically drivenfrom a truck battery or generator, or powered by energy from theexpansion of warmed pressurized nitrogen gas as described and claimed incopending application Ser. No. 643,709 filed June 5, 1967.

FIG. 2 illustrates a railroad car embodiment in which elementscorresponding to those previously described and illustrated in FIG. 1have been identified by the same numeral. Other elements which differfrom FIG. 1 are described hereinafter, along with their functions.

Thermal insulation 21a is provided around overhead spray conduit 21 toavoid product freeze damage and moisture drippage. Second liquiddischarge conduit 23 having control valve 24 communicates at oneend'with liquid nitrogen storage container 14 through first liquiddischarge conduit 15. Alternatively one end on conduit 23 may extenddirectly into liquid storage container 14 as does first conduit 15. Ineither event the other end of second liquid discharge conduit 23 joinswith heat exchanger means 25, illustrated as a vaporizer extending theend-to-end length of chamber 11 beneath floor 26 but in thermalassociation therewith. Alternatively, heat exchange means 25 could belocated above the floor at one end of the storage chamber. Althoughillustrated as one passageway, heat exchanger 25 preferably comprisestwo sections positioned on either side of the longitudinal centerline ofchamber 11, and provides sufficient heat transfer surface area to insurevaporization of the cold liquid continuously flowing thereto. This heatis supplied in large part by the warmer circulating chamber environmentgas contacting the outer surfaces of heat exchanger 25.

The discharge end of heat exchanger 25 joins external heat exchanger 27wherein the cold nitrogen fluid may be superheated by atmospheric heat.The resulting warmed nitrogen gas is returned to the product chamber 11through conduit 28 communicating with gas expander 29, which ispreferably centrally positioned in the upper portion of the chamber nearthe front end of storage chamber 11. As illustrated the front end ofchamber 11 is also the inlet end of spray conduit 21, but the conduitmight also be positioned with its discharge end at the front of chamber11 adjacent expander 29. The latter is preferably a commerciallyavailable sliding vane-type air motor with an inlet pressure of about10-25 psig. operating at ZOO-1,500 rpm. or greater, but a turbine typeexpander may be used. Expander 29 is joined by shaft coupling means 30to fan 31 also positioned near spray conduit 21, and preferably betweenthe liquid storage container 14 and the first spray opening 22a. If thedesired operating speed of fan 30 is not suitable for the driving motor29, speed change by belt drive or gears may be used.

The exhaust gas from expander 31 is preferably directed into chamber 11through the discharge port 32. Direct discharge through expander port 32at atmospheric pressure is preferred to obtain maximum pressure dropacross the expander. This in turn develops as much shaft power aspossible for driving fan 31.

Fan 31 circulates environment gas, including a portion of the coldnitrogen intermittently sprayed from openings 22, across the uppersection of chamber 11 over product 12 to the rear end thereof anddownwardly to the bottom passages beneath floor 26. The floor structuresof commercially employed product storage chambers, e.g. trucks, trailersor railcars, usually comprise wood slats or shaped metal such aschannels or corrugations which are spaced apart and shaped to provideadequate structural strength and light weight. These structures alsoprovide spaces for adequate longitudinal gas circulation under theproduct load. Cold fluid conduit 25 may be supported within suchdepressions in the floor and thermally insulated therefrom. The thermalinsulation should be sealed from the atmosphere to prevent moisturepenetration and consequent loss of efficiency. The fan circulates gasfrom end to end of the chamber 11 floor in passageways formed by suchchannels or corrugations to recover refrigeration from the liquid-vaporin conduit 25. The thus warmed environment gas rises at the chamberfront end and is at least partially recirculated by fan 31 in theaforedescribed manner. A part of this gas may be discharged to theatmosphere through vent 32a to avoid overpressuring in chamber 11.

During the winter the temperature difference between the surroundingatmosphere and the desired refrigeration level within chamber 11 issmaller than in the summer. Accordingly the combined heat exchangecapacity of internal unit 25 and external unit 27 may not be requiredduring the winter. In this event passageways 25 may be bypassed and thenitrogen liquid from second discharge conduit 23 diverted throughconduit 33 and control valve 34 therein directly to atmospheric heatexchanger 27. Under these circumstances the nitrogen liquid is bothvaporized and superheated by atmospheric heat prior to flow throughwande 9- The unexpected advantages of this invention are illustrated ina series of tests as follows.

rasrno. 1

A 45 foot long stationary railcar having thermal insulation ofsufficient quality to limit the heat inleak rate to about 0.07 Btu/hr.F.-ft. was provided with the components illustrated in'FlG. 2 and firsttested with. a '14- inch ID by 7/8-inch OD copper spray headercontaining twenty-five 1/16-inch diameter openings longitudinally spacedend-to-end. The spray header was insulated with 1 inch of urethane foamso that the fluid discharged through the openings comprised mostlyliquid. The set point for bulb 17 was F. and the crosssectional area ofthe chamber was about 86 ft Nitrogen refrigerant was sprayed into theproduct chamber at an effective flow rate of about 143 lbs./hr./10 ft.average length of chamber through the openings, having a total area ofabout 0.016. inch per 10 foot length of, chamber. The maximum flowrating was about 185 lbs/hr. .N 10 ft. average length. After observingthat the temperature distribution withinth'e chamber was undesirablyuneven, all but five of the spray openings were closed to provide totalopen area of 0.003 inch l 10 ft. average length of chamber. Theseremaining five openings were located the following distances from thespray conduit inlet end: 3.7, 13.6, 25.9, 36.1 and 44.2 feet. Therefrigerant flow rate was thereby reduced so that the refrigerant oncycle was lengthened, the spray header cooldown time became a smallerfraction of the on cycle, and the upset in temperature distribution dueto this cooldown was minimized. Another advantage of the lowerrefrigerant effective flow rate was lower pressure drop in the sprayheader which permitted maximum pressure drop (to atmospheric pressure)across the spray openings. This resulted in greater atomization of theliquid nitrogen on discharge through the openings, and more uniformdistribution of refrigeration to the product. In addition to the runswith five openings, other runs were made with six openings located thefollowing distances from the spray header inlet end: 7.4, 17.8, 27.7,34.6, 39.4 and 44.2 feet; and eight openings located the followingdistances from the spray header inlet end: 7.4, 13.6, 19.9, 25.9, 31.2,36.1, 40.4 and 44.2 feet. These runs are summarized in Table B and showthat comparable or superior temperature distribution was achieved atmuch lower maximum flow ratings per 10 ft. average length of chamber.

Five railcars equipped with $4 inch-IPS brass pipe uninsulated sprayheaders and forty-f ve l/ 16-inch diameter holes were converted tocopper spray headers yfi-inch ID X 96-inch OD insulated with 2% inchthick elastomer foam and provided with ten l/ 16-inch diameter openingsto test this invention. These railcars were provided with sufficientplastic foam thermal insulation in the walls to limit the heat transferinleak rate to about 0.07 Btu/hr.F.-ft*, and used to transport andrefrigerate fresh produce such as lettuce, plums, cauliflower andavocados. The operating data is suma ized in T bLqC,

TABLE C I max. LN, total area of flow rating average number holeseffective per 10 it. product spray in'/ 10 ft. LN, flow Igth. avg.temperature holes lgth. avg. rate lb/hr. lbs/hr. deviation 'F 45 0.0401200 470 3-5 10 0.009 270 100 2-4 TEST NO. 3

A 37 foot long chamber of ft 'cross-sectional area equipped withapparatus similar to FIG. 2 but comprising a tractor-pulled trailer wasused .to transport fresh lettuce from Blythe, Califomia' toTonawanda,-New York overv a seven-dayperiod-during the month of Decemberwith a 35F. set point. The trailer was provided with sufficient plasticfoam thermal insulation to rate system. The data from these runs issummarized in Table D.

TABLE D Max. LN, Total Area of Flow Rating Average Number HolesEffective per 10 ft. product spray in'llO ft. LN, Flow lgth. avg.Temperature Holes lgth. avg. Rate l b/hr. lbs/hr. Deviation "F 32 0.026850 330 5-10 10' 0,008 270 109 3-4 TEST NO. 4

A series of runs were made using a product storage chamber in the formof an insulated truck similar to FIG. 1, about 48 ft cross-sectionalarea and about 17.5

, feet long. The truck was insulated with nominal 3 inch polyurethanefoam to provide a heat inleak rate of about 0.05 Btu/hr-Fft The productwas frozen food and the set points were +10F. and 5F. Periodic stopswere made to unload the frozen food, first using a conventionaluninsulated spray header having ten l/ l 6- inch diameter openings(0.018 in l 10 ft. length average) and then with another spray headeraccording to this invention with six 3/64-inch diameter openings (0.006m 10 ft. length average). The latter spray header consisted of two 57inch long sections of A-inch IPS brass pipe connected by a 24 inch blanksection. The spray header was side-mounted near the chamber ceiling 33inches from the chamber front end, and the 3/64-inch'diameter openingswere located the following distances from the inlet end:

fl Dislance (gwhes) modifications of the method and apparatus may be 2r9 made and that some features may be employed without 3 34 others, allwithin the spirit and scope of the invention. g 33 For example theinvention may be used for stationary 6 136 refrigeration systems as wellas in-transit systems.

What is claimed is: The data from these runs 18 summarized in Table Eas 1. Apparatus for refrigerating perishable products follows:comprising in combination:

TABLE E Average Overall Efiec- Max. LN2 Opening area, Total ambient Lbs.LN; tlve LN2 flow-rat- 1 it. run, N0. temp., LNZ/ rate, flow rate,iug/IO it. lgth. avg. hrs. stops F. stop lb./hr. lbJhrr lgtli. avg.

For the above four runs the set point temperature was +10 F.

0.000 8.8 0 62 23.0 24. a 94 85 0.013 0.0 is 04 25. s as. e are 265 Thefrozen products refrigerated by each system were delivered insubstantially the same satisfactory condition. It is apparent from TableE that the nitrogen a. a storage chamber for said perishable productshaving thermal insulation sufficient to limit heat inlead rate below0.10 Btu/hrF-ft and crossspray refrigeration system of this inventionpermitted a s ti n area tw 40 d 1 very significant reduction inrefrigerant consumption at a thermally insulated container associatedwith the no loss in performance, indicating that the refrigerant storagechamber for holding pressurized nitrogenwas used more effectively. richliquid;

TEST N0 5 c. spray conduit means positioned within the upper portion ofsaid storage chamber and extending Another group of ,runs was made theSame substantially the entire length thereof with product e e as m e 3but wlth a spray openings of equivalent diameter less than 0.07 headerhaving eight 0.038 mch diameter holes (0.005 inch Spaced along thelength for discharging a inzlm length avg)- These hole? were Spaced thetiplicity of discrete cold fluid streams into the lowing distances fromthe header inlet end: storage chamber for f i ti Same, said openingshaving total area of between 0.002 and Number Disiance (21cm) 4 0.009 inper 10 ft average length of chamber;

2 21 d. fluid discharge conduit means communicating at i is one end withthe liquid container and at the other 5 as end withsaid spray conduit; e103 7 118 e. fluid flow control means comprising a temperature 8 129sensing element positioned within said storage chamber, and a controlvalve operably interposed The Set POint was again and the p was in saidfluid discharge conduit means being confrozen food, cg. boxedvegetables, meat and canned nected to said temperature sensing elementto be fruit juices. The data from these runs is summarized in responsiveto the storage chamber gas temperature Table F as follows: as sensed bysuch element.

TABLE F Avg. Overall Effective Max. LN2 Opening area, Total ambient Lbs.LNZ use LN; flow flow rating/ inJ/IO it. run, No. temp, LNz/ rate, rate,10 It. lgtli. avg. hrs. stops F. stop 1b./hr. lbs/hr. lgth. avg.

0.005 as 0 so 22.5 15.3 67 0.018 0.0 6 60 30.2 283 2. Apparatusaccording to claim 1 in which thermal insulation is provided around saidspray conduit means.

3. Apparatus according to claim 1 in which the openings are of about0.038 inch diameter and circular.

4. Apparatus according to claim 1 in which the spray conduit meanscomprises multiple sections of %-inch IPS pipe 57 inches long eachhaving four 0.038 inch diameter circular holes spaced respectively 10,21, 36 and 51 inches from one end.

5. Apparatus according to claim 1 in which the total 3 ,705 ,5 1 14marea of said openings is between 0.004 and 0.008 inch positioned withinthe storage chamber at one end per foot average length of chamber.thereof to circulate environment gas. 6. Apparatus according to claimljn which a fan is :r

} UNITED STATES PATENT OFFICE CERTIFIGATE' OF CORRECTION Pate: No, I sue Date December 12 lnventofls) R. Jehle It is certified that errorappeara in'the above-1dent1fied patent and that said Letters Patent arehereby corrected as shown below:

Claim 1(a) line 24, delete "inlead" andsubstitute --inleak--.

Signed and sealed this 1 st day of May 1973.

(SEAL) Attest: EDWARD M. FLETCHER, JR. ROBERT GOTTSCHAIK AttestingOfficer Commissioner of Patents Pat 212= +.72

1. Apparatus for refrigerating perishable products comprising incombination: a. a storage chamber for said perishable products havingthermal insulation sufficient to limit heat inlead rate below 0.10Btu/hr-*F-ft2 and cross-sectional area between 40 and 100 ft2; b. athermally insulated container associated with the storage chamber forholding pressurized nitrogen-rich liquid; c. spray conduit meanspositioned within the upper portion of said storage chamber andextending substantially the entire length thereof with openings ofequivalent diameter less than 0.07 inch spaced along the length fordischarging a multiplicity of discrete cold fluid streams into thestorage chamber for refrigerating same, said openings having total areaof between 0.002 and 0.009 in2 per 10 ft average length of chamber; d.fluid discharge conduit means communicating at one end with the liquidcontainer and at the other end with said spray conduit; e. fluid flowcontrol means comprising a temperature sensing element positioned withinsaid storage chamber, and a control valve operably interposed in saidfluid discharge conduit means being connected to said temperaturesensing element to be responsive to the storage chamber gas temperatureas sensed by such element.
 2. Apparatus according to claim 1 in whichthermal insulation is provided around said spray conduit means. 3.Apparatus according to claim 1 in which the openings are of about 0.038inch diameter and circular.
 4. Apparatus according to claim 1 in whichthe spray conduit means comprises multiple sections of 1/4 -inch IPSpipe 57 inches long each having four 0.038 inch diameter circular holesspaced respectively 10, 21, 36 and 51 inches from one end.
 5. Apparatusaccording to claim 1 in which the total area of said openings is between0.004 and 0.008 inch2 per 10 foot average length of chamber. 6.Apparatus according to claim 1 in which a fan is positioned within thestorage chamber at one end thereof to circulate environment gas.